The B+W 77mm 81B Filter is a colour conversion filter that helps to slightly decrease colour temperatures and provide a warming effect. The 81B filter adds more warmth to the image for use with tungsten films in natural lighting. It provides a decrease of 300K, helping to render the scene more similarly to incandescent illumination.

There is a 1.5x filter factor with this filter, requiring an increase of 0.6 stop for normal exposure. B+W filters are constructed from high quality Schott glass for increased optical clarity and colour fidelity. They feature a brass filter ring for durability as well as jamming prevention.